In manufacturing semiconductor devices such as LSI and super-LSI or in manufacturing a liquid crystal display board or the like, a pattern transferring is conducted by irradiating light to an exposure original plate such as a semiconductor wafer or an original plate for liquid crystal, but if a dust particle exists adhering to the exposure original plate, the dust particle absorbs the light or refracts it, giving rise to deformation of a transferred pattern and roughened edges, which lead to problems such as a damaged dimension, a poor quality and a deformed appearance, lowering the performance and the manufacture yield of the semiconductor devices and the liquid crystal display board.
Thus, these works are usually performed in a clean room, but it is still difficult to keep the exposure original plate in a dust-free state all the time; therefore, a pellicle, which transmits the exposure light well, is attached to a surface of the exposure original plate as a dust-fender.
Under such circumstances, dust does not directly adhere to the surface of the exposure original plate but only onto the pellicle membrane, and thus, in lithography operation, by setting a photo focus on the pattern formed on the exposure original plate, the dust particles on the pellicle membrane fail to cast their shadows in the image transfer performance.
A pellicle is built up of a pellicle frame, which is usually made of aluminum or a stainless steel or polyethylene or the like, and a transparent pellicle membrane usually made of cellulose nitrate or cellulose acetate or a fluorine-containing resin or the like, which transmits light well; this membrane is attached to one of the two annular face of the frame (hereinafter referred to as “upper annular face”) after laying a solvent capable of dissolving the pellicle membrane on the upper annular face and drying the solvent by air flow (ref. Publication-in-IP 1), or after laying an adhesive such as acrylic resin and epoxy resin (ref. Publications-in-IP 2, 3 and 4); furthermore, on the other one of the two annular faces of the frame (hereinafter referred to as “lower annular face”) is laid an adhesive layer made of a polybutene resin, a polyvinyl acetate resin, an acrylic resin, a silicone resin or the like, and over this adhesive layer (hereinafter also referred to as “agglutinant layer”) is laid a releasable liner (separator) for protecting the agglutinant layer.
In recent years, the requirement for the resolution of lithography has become heightened gradually, and in order to attain such higher resolutions the light sources having shorter and shorter wavelengths have come to be adopted. In practice, ultraviolet lights [g-line (436 nm), i-line (365 nm), KrFexcimer lasers (248 nm)] are newly employed, and more recently ArFexcimer lasers (193 nm) have begun to be used.
However, as the wavelengths of the exposure lights are shifted toward zero side, a new problem has arisen wherein a deformation of the lithographic image is caused by the deformed flatness of exposure original plate (mask).
It has been pointed out that one of the causes for the deformation of the flatness of the exposure original plate is the less admirable flatness of the pellicle which is attached to the exposure original plate.
The inventor hereof previously presented a proposal for controlling the mask deformation caused by pellicle attachment to the mask by means of an improvement in the flatness of the mask-bonding agglutinant layer (ref. Publication-in-IP 5).
In this Publication-in-IP 5, it is proposed to make flatter the surface of the mask-bonding agglutinant layer laid on an annular face of the pellicle frame by pressing the pellicle frame on a flat plate having a high flatness by the weight of the pellicle frame itself.
That invention certainly improved the maintenance of the high flatness of the mask greatly; however, there have still been occasional incidents observed wherein the transferred light image was deformed, especially in the cases wherein the masks are exposed to lights of shorter wavelengths. The cause for this deformation was looked for and it was found that when applied to the mask surface the agglutinant layer undergoes a deformation and this deformation is maintained by the power of the layer's adhesiveness and thereby a deformation stress in retained internally.
Thus, when the pellicle is being attached to the mask, the membrane-side face of the pellicle is touched with pressure by a pressure plate of a pellicle mounter (whereby the pellicle frame becomes more flatted), and on this occasion, if the membrane-bonding adhesive layer has an unevenness, the convex parts are pressed with greater forces than the concaved parts are. Then, even if the (mask-side) surface of the agglutinant layer is finished sufficiently flat, that part of the agglutinant layer which corresponds to the convex part of the adhesive layer receives more pressure, and as the result the side faces of the agglutinant layer receiving greater pressure bulge (creep) and thereby get in contact with the mask.
When the pressure plate is removed from the pellicle after the pressing operation is over, the pellicle frame freed from the pressure tries to revert to its former shape (which is comparatively more deformed than when under pressure). Thus as the pressure plate is removed and the pressure is gone the pellicle frame deforms again but as the agglutinant has a certain degree of adhesion strength, that part of the agglutinant which has bulged and contacted with the mask keeps sticking to the mask without returning to the former position, and as the result to compensate this the mask is pulled by the pellicle frame especially strongly at such bulged agglutinant portions, and thus the mask is deformed tracing the deformation of the pellicle attached thereto.